The objective of the Sheep Core is to provide a mechanism whereby the services of common personnel are shared by all projects of this Program Project Grant, enabling cost-effective breeding and animal maintenance programs of exceptionally high standards. The underlying rationale for this Core is simple. A staff of well-qualified individuals can meet the needs of multiple research projects more effectively and economically than if each project were to meet its needs separately. This is especially important given that a major function of this core will be to generate sheep that have been programmed prenatally by exposure to gonadal steroids at known stages of pregnancy. This requires extensive experience and expertise of managing fertility, breeding, and early postnatal care in this experimental species. The Specific Aims of the Sheep Core are as follows. Specific Aim 1. To operate a breeding program to generate sheep that are prenatally treated with gonadal steroids at specific fetal ages and vehicle-treated control sheep for use by the three research projects that make up this Program Project Grant. Specific Aim 2. To coordinate effective and economical usage of sheep by three interrelated research projects. Specific Aim 3. To provide a uniform and high standard of animal maintenance and veterinary care. Specific Aim 4. To provide a technical knowledge base for reproductive research in sheep. By achieving these aims, the Sheep Core will greatly enhance the productivity of all projects in the Program Project Grant.